Pallet wrapping using structural plastic film in various methods is well known in the packaging art. Various machines and apparatus are used to place plastic film about a palletized load. Generally, the method employed involves dispensing a plastic film from a film reel and helicoidally placing the film about the load. The film improves the cohesiveness of a palletized load, thereby preventing elements of the load from being displaced. This increases safety in the work environment preventing falling objects or spilled loads and increases material-handling efficiency. Wrapping a load also works to protect the elements therein from the outside environmental influences such as water and dust.
However, it has been found that it is not practical to wrap certain types of loads in the manner described above. Since no spacing is left between adjacent strips of film in the above-described wrapping operation, air is not allowed to circulate to the individual elements stacked within the palletized load. This can be very detrimental to palletized loads containing foodstuffs such as fresh produce, hot-wrapped products or products palletized in a freezing environment. Each of these type of loads require air spacing between plastic film strips in order to allow the products to "breathe." Without such air spaces, condensation will usually form in the interior of the load inside the plastic wrap. This condensation encourages and hastens the spoiling of certain food stuffs. Additionally, hot-wrapped products are not allowed to cool properly. This can be detrimental to the product itself and, additionally, can be detrimental to the integrity of the wrapped load since uncontrolled heating and cooling of the film material can change the composition and strength properties of the plastic film wrap. Moreover, products which are palletized in a freezing environment will necessarily thaw during warming give up moisture that had previously condensed during cooling. Depending on the products contained therein, this condensation may result in spoiling of the product. Additionally, condensation may destroy the integrity of corrugated boxes or other packaging elements which comprise the palletized load.
A number of solutions have been proposed in order to allow palletized loads to "breathe." The most common of these solutions is to place a netting about or around the palletized load. While netting allows a product to "breathe", it has other inherent problems. The most obvious of these problems is that netting is not inherently adaptable to automatic wrapping of a load. Therefore, it is labor intensive, time consuming and expensive. Further, netting does not have the advantageous property of plastic film wrap, notably the capacity of stretching elastically and being adhesive to at least other strips of plastic film wrap. As a result, netting does not have the cohesive holding quality of plastic film and thus a palletized load covered with netting is not as durable and is more susceptible to individual elements coming free from the load. Finally, netting is easily snagged by passing objects as a palletized load is moved from one position to another. Snagging just one portion of the netting can result in an entire load being pulled from a pallet.
It has also been proposed to package a load by taking packaging film and cutting it into strips of reduced width. Each strip of reduced width is then wound about a load such that spaces are left therebetween to allow the package to "breathe." Such a solution is not advantageous in that individual strips of film of reduced width are weak and susceptible to stresses and tension. Therefore, only slight resistance when winding such narrow strips of film often results in breaking of the film. Because of this weakness, the film cannot be wrapped with the tension which would otherwise be desired and thus the load is not advantageously unitized. Since each strip is narrow, this method also increases the amount of time required to wrap each load.
Another proposed method has been to reduce the width of a film strip by reducing the flat section into a narrow rope or cord. This has the advantage of increasing the tensile strength of the film since, while the width is reduced, the thickness of the film is increased. However, such method has the disadvantage of substantially increasing the material cost to wrap a singular load in that the entire width of film is reduced to one rope or cord. Furthermore, such a method does not always properly secure individual element products to the pallet. The individual cords do not provide a sufficient width to secure the products and are often placed varying distances from each other wherein certain individual elements of the load are not secured at all. Moreover, such a wrapping method substantially increases the amount of time required to wrap a singular load. The bunching of a large width of film into a rope or cord is also undesirable in appearance and increases the susceptibility of the film catching or snagging on adjacent objects as a load is moved from place to place.
Ropes or cords of plastic film also present problems in attaching the end of the film to the load. As is often the case, a section of roped plastic film does not have the adhesive quality that the entire width of film has when placed on a load. It is therefore necessary to gather a cord together at the end and tie it off to the load or to the pallet. This is time consuming and labor intensive and severely reduces the economic advantage of roping a palletized load. When it is necessary to wrap palletized loads in a steady constant and cyclical manner, the roping operation described above becomes impractical.
Finally, it has been proposed to wind the full width of film to secure the lower part of the goods on the pallet and subsequently to cut the film into strips. These strips are then wound about the load, strips having spaces therebetween and, before the wrap is finished, the cutting operation is stopped and the full width of the film is restored so that the full width of the film may be wound about the upper part of the goods for at least one turn. While this method corrects many of the problems inherent in the prior art, it also presents other problems. For instance, cutting the film web into strips has presented problems in that the film web is stretchable and elastic. Often the cutting mechanism does not actually cut the film but instead only creases the film web. The elasticity of the film also causes bunching at the cutting edge, inaccurate cutting and tearing of the film web. Further, the proposed method requires the use of a full web of film at both the top and bottom of the pallet. The use of a full web effectively seals both the top and bottom layers of a palletized load within a non-breathable film strip. This is undesirable for all the reasons set forth above. Specifically, fresh produce in the top and bottom layers will more easily spoil since condensation cannot escape, hot-wrapped products are unable to cool properly and products palletized in a freezing environment are unable to thaw properly.